<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>上+中（分三列，中间列是侧边的2倍宽）布局</title>
    <style>
        * {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
        }

        body {
            font-family: Arial, sans-serif;
        }

        .row {
            width: 100%;
            overflow: hidden;
        }

        .column {
            float: left;
            padding: 20px;
            box-sizing: border-box;
        }

        .header,
        .footer {
            background-color: #f0f0f0;
            text-align: center;
        }

        .content {
            background-color: #f9f9f9;
        }

        .left,
        .right {
            width: 25%;
        }

        .center {
            width: 50%;
        }

        /* 使中间列宽度为侧边列的两倍 */
        .left,
        .right {
            width: 25%;
        }

        .center {
            width: 50%;
            background-color: aqua;
        }
    </style>
</head>

<body>
    <div class="row header">
        <h2>上</h2>
    </div>
    <div class="row content">
        <div class="column left">
            <h2>侧边</h2>
        </div>
        <div class="column center">
            <h2>中间</h2>
        </div>
        <div class="column right">
            <h2>侧边</h2>

        </div>
    </div>
    <div class="row footer">
        <h2>下</h2>
    </div>
</body>

</html>